backend v2.1: 公告管理功能 + 系统重构

- 新增 Announcement 数据模型，支持公告的增删改查
- 后台管理新增"公告管理"Tab（创建/编辑/删除/启用禁用）
- 客户端 /api/announcement 改为从数据库读取
- 账号服务重构，新增无感换号、自动分析等功能
- 新增后台任务调度器、数据库迁移脚本
- Schema/Service/Config 全面升级至 v2.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/config.py

@@ -8,20 +8,20 @@ class Settings(BaseSettings):
     DB_HOST: str = "127.0.0.1"
     DB_PORT: int = 3306
     DB_USER: str = "cursorpro"
-    DB_PASSWORD: str = "jf6BntYBPz6KH6Pw"
+    DB_PASSWORD: str = ""
     DB_NAME: str = "cursorpro"
 
     # JWT配置
-    SECRET_KEY: str = "hb8x2kF9mNpQ3rT7vY1zA4cE6gJ0lO5sU8wB2dH4"
+    SECRET_KEY: str = ""  # Must be set via .env
     ALGORITHM: str = "HS256"
     ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 7  # 7天
 
     # 管理员账号
     ADMIN_USERNAME: str = "admin"
-    ADMIN_PASSWORD: str = "Hb@2024Pro!"
+    ADMIN_PASSWORD: str = ""
 
     # 外部系统API Token (用于批量上传账号等)
-    API_TOKEN: str = "hb-ext-9kX2mP5nQ8rT1vY4zA7c"
+    API_TOKEN: str = ""
 
     @property
     def DATABASE_URL(self) -> str: